Cooling for PMA (Perpendicular Magnetic Anisotropy) Enhancement of STT-MRAM (Spin Torque Transfer-Magnetic Random Access Memory) Devices

ABSTRACT

A fabrication process for an STT MTJ MRAM device includes steps of cooling the device at individual or at multiple stages in its fabrication. The cooling process, which may be equally well applied during the fabrication of other multi-layered devices, is demonstrated to produce an operational device that is more resistant to adverse thermal effects during operation that would normally cause a similar device not so fabricated to lose stored data and otherwise fail to operate properly.

BACKGROUND 1. Field of the Invention

This invention relates generally to a spin-torque transfer random accessmemory (STT-MRAM) device and to the application of thermal cooling tofabrication processes as a method of improving device performance.

2. Description

A critical aspect of MRAM performance is thermal stability, the abilityof a device to maintain stored information stable against temperaturevariations without refreshing or other external help. It is especiallyimportant as the MTJ (magnetic tunnel junction) unit cell size scalesdown for advanced CMOS (complementary metal-oxide semiconductor)technology nodes since the thermal stability is proportional to the MTJsize in theory and positively correlated with the MTJ size in reality.In addition, some standard semiconductor assembly processes will exposethe CMOS chips to high temperatures (260 C for example), with whichMRAM, as a candidate for embedded memories, needs to comply. At suchtemperatures, the traditional thinking that thermal stability is solelythe requirement of the free layer of a MTJ no longer applies. First, thetemperature dependence of the thermal MTJ stability can be different forthe free layer and the pinned layer as they may consist of differentmaterials. Since the fabrication processing temperature is so much abovethe normal temperature range for typical data retention concerns, onecannot say the pinned layer has better thermal stability than free layersimply because it is within chip working temperature range (typicallyless than 125 C or 150 C) without additional study. More importantly,the free layer is normally at or near a balanced dipole field from theSynthetic Anti-Ferromagnetic (SAF) pinned layer, whereas the pinnedlayer is not. As temperature increases and coercivity field decreases,the difference between balanced and unbalanced dipole field can have abig influence on the thermal stability. As a result, one needs toconsider thermal stabilities for both the free layer and pinned layerfor embedded MRAM applications that follow the standard semiconductorproduct procedures.

As the film stacks for working MRAMs become more and more complicatedand each functional layer tends to be formed of multiple layers ofdifferent materials for better performance, a single stack layer (i.e. alayer deposited using one set of deposition tool parameters, includingtargets, chamber pressure, gases and flow rates) is often ultra-thin,consisting only a few mono-atomic layers (a few Angstroms) of certainmaterials deposited across a 200 mm˜300 mm wafer. At this level, thefilms deposited in the MTJ stack have quite different properties thanbulk materials and the deposition conditions can significantly changethe morphology of the film, thus impacting the total MTJ performance,including thermal stability.

The conventional magnetic tunneling junction (MTJ) device is a form ofultra-high magnetoresistive device in which the relative orientation ofthe magnetic moments of parallel, vertically separated, upper and lowermagnetized layers controls the flow of spin-polarized electronstunneling through a very thin dielectric layer (the tunneling barrierlayer) formed between those layers. When injected electrons pass throughthe upper layer their spins are polarized by interaction with themagnetic moment of that layer. The majority of the electrons emergepolarized in the direction of the magnetic moment of the upper layer,the minority being polarized opposite to that direction. The probabilityof such a polarized electron then tunneling through the interveningtunneling barrier layer into the lower layer then depends on theavailability of states within the lower layer that the tunnelingelectron can occupy. This number, in turn, depends on the magnetizationdirection of the lower electrode. The tunneling probability is therebyspin dependent and the magnitude of the current (tunneling probabilitytimes number of electrons impinging on the barrier layer) depends uponthe relative orientation of the magnetizations of magnetic layers aboveand below the barrier layer. The MTJ device can therefore be viewed as akind of multi-state resistor, since different relative orientations(e.g. parallel and antiparallel) of the magnetic moments will change themagnitude of a current passing through the device. In a common type ofdevice configuration (spin filter), one of the magnetic layers has itsmagnetic moment fixed in direction (pinned) by exchange coupling to anantiferromagnetic layer, while the other magnetic layer has its magneticmoment free to move (the free layer). The magnetic moment of the freelayer is then made to switch its direction from being parallel to thatof the pinned layer, whereupon the tunneling current is large, to beingantiparallel to the pinned layer, whereupon the tunneling current issmall. Thus, the device is effectively a two-state resistor. Theswitching of the free layer moment direction (writing) is accomplishedby external magnetic fields that are the result of currents passingthrough conducting lines adjacent to the cell.

One of the deposition parameters that greatly influences the filmproperty is the temperature of the wafer, which is a result of the factthat films grown on the wafer are generally the product of sputtering ofvarious atomic species onto that wafer. When the sputtered speciesarrive at a cold surface, they tend to move and (or) penetrate less andvice-versa for arrival at a hot surface. Therefore, the result of thesputtering process depends on the affinity of the material beingdeposited and the material previously deposited. Using this fact, onecan “tune” or adjust the wafer temperature to obtain some desiredmorphology (coverage, grain size, etc.) for the newly deposited film.This understanding leads us to the proposition that the very factorsthat challenge thermal stability of an operating device also play a rolein the factors that affect the fabrication of that device. Thisunderstanding has led us and some of those in the prior art to suggestthat thermal conditions that exist during device fabrication can affectthe thermal stability of the final fabricated device. Examples of priorart attempts to regulate thermal conditions during fabrication tomitigate poor operational characteristics in the final device includethe following.

U.S. Pat. No. 9,761,795 (Park et al.) discloses cooling a substrate in acooling chamber to 50-300 K after the pinned layer is formed and beforethe MgO layer is formed. Cooling is by introducing a refrigerant intothe chamber.

U.S. Patent Application 2013/0216702 (Kaiser et al.) teaches cooling asubstrate in a cooling chamber to 50-293 K before or after part of thefree layer has been formed.

U.S. Patent Application 2016/0130693 (Sawada et al) teaches cooling asubstrate in a cooling chamber to room temperature before depositing atunnel barrier layer.

U.S. Application 2016/0099288 (Watanabe et al) states that it isdesirable for a cooling process to be performed before formation of therecording layer.

We have found that none of these approaches produce the results of themethod to be disclosed herein.

SUMMARY

A first object of this disclosure is to provide an MRAM device withimproved stability under thermal variations, i.e. the ability tomaintain storage of data without refreshing cycles or other externalassistance.

A second object of this disclosure is to provide such an MRAM device bymeans of a method of fabrication that lowers temperatures of the devicebeing fabricated during certain portions of the fabrication process.

A third object of this disclosure is to address the issue of thermalstability by application of processing methods that will have the mostadvantageous affects on the properties of the thin films that aredeposited on the wafers.

As we have noted above, one of the deposition parameters that greatlyinfluences the film property is the temperature of the wafer. When asputtered species arrives at a cold surface, it tends to move and (or)penetrate the surface less and vice-versa for arrival at a hot surface.Therefore, the result of the sputtering process depends on the affinityof the material being deposited and the material previously deposited.Using this fact, one can “tune” or adjust the wafer temperature toobtain some desired morphology (coverage, grain size, etc.) for thenewly deposited film.

We find that by depositing part of the pinned layer at cool temperaturein one of our presently used stacks, the thermal stability of the pinnedlayer, and therefore that of the chip as a whole, increasessignificantly and measurably.

This cooling is achieved inside a special cooling chamber within thedeposition tool. After the initial part of the pinned layer deposition,the wafer is transferred in ultra-vacuum to the cooling chamber. It isthen clamped to a cold stage (60 K) inside the chamber for certainperiod of time. The actual wafer temperature will decrease in thebeginning of this process and reach a steady temperature close to thatof the stage after approximately 200 s. Then the wafer is quicklytransferred, while still in the ultra-vacuum, to the deposition chamberfor the rest of the pinned layer deposition. The wafer temperature willslowly increase while still remaining cold during the rest of the pinnedlayer deposition.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of an MTJ MRAM stack that has beenfabricated using the cooling process described herein.

FIG. 2 is a schematic representation showing the first step in thefabrication of the MTJ MRAM stack of FIG. 1.

FIG. 3 is a schematic representation showing the second step in thefabrication of the MTJ MRAM stack of FIG. 1.

FIGS. 4A-4C are a schematic representation showing three successiveprocesses required to form a layer on the cooled fabrication during thethird step in the fabrication of the MTJ MRAM stack of FIG. 1.

FIG. 5 is a schematic representation showing the fourth step in thefabrication of the MTJ MRAM stack of FIG. 1.

FIG. 6 is a schematic representation showing the fifth step in thefabrication of the MTJ MRAM stack of FIG. 1.

FIG. 7 is a schematic representation showing the sixth step in thefabrication of the MTJ MRAM stack of FIG. 1.

FIG. 8 is a schematic representation showing the final step in thefabrication of the MTJ MRAM stack of FIG. 1.

DETAILED DESCRIPTION

A preferred embodiment of the present disclosure is the fabrication ofan exemplary STT MTJ MRAM cell fabricated with the imposition oftemperature reduction (i.e., cooling) during any individual one ofseveral steps in the process, or during several of the steps. We notethat the process is by no means limited to the fabrication of anexemplary device such as this cell, but this particular device is one ofimportance in the industry and includes many commonly appliedfabrication techniques, so the cooling process can be widely tested. TheMRAM exemplary device is an MTJ layered structure (an unpatterned stack)that, upon completion, comprises the sequence of deposited layers shownschematically in FIG. 1. In FIGS. 2-8 we will describe and illustratethe nature of the individual deposition and cooling processes thatultimately create the stack in FIG. 1. We limit the fabrication processto be described using FIGS. 2-8 below to the application of a coolingstep at one particular point in the fabrication, which is a step duringthe formation of the AP1 layer in a SAF (Synthetic Antiferromagnetic)pinned layer. In this step, the AP1 layer is being formed as twosuccessively deposited layers, 44 and 42, and a cooling step isperformed on layer 42 so that layer 44 can be deposited on cooled layer42. It is to be understood that the cooling step can be performed atmany other stages in the fabrication and the figures describing themwould only differ in where the step is performed.

Referring then to FIG. 1, there is shown, schematically, the followingfinal sequence of fabricated layers, whose individual properties will bediscussed below. A wafer substrate 5 is provided as the base upon whichthe subsequent layers are fabricated. The substrate has been patterned(patterning not shown) to provide a surface region on which to fabricatethe subsequent layers. The substrate will be removably affixed tovarious stages in the sputtering/deposition subsystem of a vacuum-sealedmulti-chamber system that includes separate chambers configured forvarious types of depositions and processing. The multi-chamber systemalso includes a temperature-reducing thermal processing subsystem. Wewill describe this system in a bit more detail below.

On the substrate 5 there is formed a layer 7 of Ta or a conductingnitride such as TiN that is then surrounded by SiO2 and the whole issmoothed by a CMP (chemical mechanical polishing) process. This willafford a good contact for a subsequently deposited seed layer 10, onwhich is further formed a synthetic anti-ferromagnetically coupled (SAF)pinned layer 55, whose coupling is maintained by the RKKY(Ruderman-Kittel-Kasuya-Yosida) interaction. This coupled pinned layersystem 55 itself comprises three layers: lower layer AP2, 20, RKKYinteraction (or coupling) layer 30 and upper double layer AP1, 42/44.Note that AP1 layer is here formed of two sequentially deposited layers,denoted 42 and 44 which will be discussed further with respect to FIG.4A-4C, below. The magnetic moments of layers AP1 and AP2 are held in anantiparallel configuration, perpendicularly to their planes of formationby the action of the RKKY interaction, which is facilitated by couplinglayer 30 whose effect to couple magnetic moments between adjacentmagnetic layers is well known in the art. The designation, using theterms AP1 and AP2 to the two layers, is simply to indicate, by thenumeral “1”, the closeness of AP1 to the tunneling barrier layer, 50,which in this example is a layer of MgO formed on layer AP1, but othermetal oxides are possible. Layer AP2 is further from layer 50. Next, aferromagnetic free layer 60 is formed on the tunneling barrier layer;following which a MgO capping layer 70 is formed on the free layer and ahard mask layer 80 is formed on the capping layer, the hard mask layerto be used in subsequent patterning steps of the completed stack. Asstated above, these individual layers are successively formed bysputtering processes inside a multi-chamber system in which one chamberis dedicated to cooling the wafer with no sputtering/depositioncapability and several other chambers are used for specificsputtering/deposition processes. The cooling process is carried out bytransferring the fabrication to the cooling chamber, when cooling isdesired, and attaching it by clamps to a metal stage which istemperature-fixed at 60K by flowing Ar gas at that temperature on it.This is illustrated in FIG. 4B below. Cooling of the fabrication occursquickly by contact with the stage and, in the present process occurs in200 seconds and stabilizes thereafter. When the cooled temperature isachieved, the fabrication is transferred to the specific separatechamber in which the deposition is to be carried out at ambient. It isnoted that the system being used for these processes is commerciallyavailable (CANON ANELVA C7100) and it provides for easy transferencebetween the cooling chamber and any one of the deposition chambers.Basically, the system, which is not shown, consists of a centraltransfer unit from which six satellite chambers radiate out, wherein onesatellite chamber provides a cooling facility and the remainder providefacilities for producing various layer depositions. When the fabricationis transferred to the cooling chamber it is clamped to a metal stage onwhich a good thermal contact is made and the entire fabrication is thencooled by a gas transfer process. When the fabrication reaches thedesired temperature, it is removed and transferred to one of thedeposition chambers where it is re-fastened to a chuck and the requireddeposition proceeds while the fabrication remains well within a desiredcooled temperature range. Once placed in a chamber in which thedeposition process is to occur, the fabrication is no longer beingactively cooled so its temperature will slowly rise to ambient. However,because of the slow rise of temperature, the deposition process iseffectively carried out on the fabrication at the desired lowtemperature (60K here). The system and others like it are known in theart, so no further detailed description will be provided herein.

Referring now to FIG. 2, there is schematically illustrated the firststep in a series of fabrication processes that are occurring within themulti-chamber system described above within which all processes can bemaintained under vacuum and, where necessary, temperature-controlledconditions. Note that each cooling step occurs in the cooling chamber ofthe system. We begin our description of this exemplary process with thecooling being carried out only at one particular step in the overallfabrication. This single cooling step process can also be applied atother points in the fabrication, and will also be described. Inaddition, several cooling steps during a single fabrication can also beapplied. After the fabrication is affixed to a stage in the coolingchamber (shown in FIG. 4B) and cooled, it is transferred back to achamber at ambient temperature that is designed for whatever depositionprocess then occurs. The deposition process is, therefore, applied tothe fabrication that is already cold, but is no longer actively beingcooled.

Referring back to FIG. 2, a substrate 5 is provided that has beenpatterned (not shown here) to create a surface region on which the MTJstack will be fabricated. On this patterned substrate 5, a layer 7 of Taor the conducting nitride TiN is deposited by sputtering with athickness of a few hundred Angstroms (A) with 400 A being typical. Thesurrounding region is filled with SiO2 and the entire region is thensmoothed with an oxide CMP process. A seed layer 10 of NiCr betweenapproximately 30 A and 100 A thickness is then deposited on layer 7which will seed AP2 layer 20, which is a repeated Co/X multilayer, withgood lattice growth along the (111) direction. Here X can be chosen fromNi, Pt or Pd, and the individual layers (i.e., Co, X) are typicallybetween approximately 1 A and 10 A in thickness. This multilayeredstructure will provide PMA (perpendicular magnetic anisotropy) for theentire stack as a result of the repeated interfacial interactionsbetween the layers. In addition, as a result of the RKKY interaction,the AP2 layer will couple anti-ferromagnetically with the AP1 layer,producing oppositely directed magnetic moments perpendicular to theirplanes of deposition.

Referring now to FIG. 3, we see the deposition of the RKKY interactionlayer 30, which may be a layer of Ru of thickness between approx. 3.5and 4 A, Ir of thickness between approx. 4.5 and 5.5 A or Mo ofthickness between approx. 5 and 6 A, which provides theanti-ferromagnetic coupling interaction between the AP2 and AP1 layersthat results in an antiparallel orientation of their magnetic moments.

Referring next to FIGS. 4A-4C, there is shown the fabrication of the AP1layer, which is here formed as the following two layers:

(i) a thin, phase-breaking generally amorphous layer 42 at the bottom tobreak the (111) crystal structure of the AP2 layer from the (001)crystal structure of the rest of the [AP1/MgO barrier/free layer]structure, while they remain magnetically connected through the RKKYinteraction, and

(ii) a CoFeB layer 44 at the top that will contact the MgO barrier layer50.

Referring first to FIG. 4A there is shown the formation of layer 42, asin (i) above, while the fabrication remains at ambient temperature inthe chamber in which layer 30 has been formed.

Referring next to FIG. 4B there is shown the fabrication, now includingjust-deposited layer 42, transferred to the cooling chamber, wherein thefabrication is placed on a metal stage 3, removably clamped to the stage4 and cooled by thermal contact to that stage, which is itself cooled bya gas flow 2, to the desired 60K temperature.

Referring now to FIG. 4C, there is shown the cooled fabrication, nowshown transferred back to a deposition chamber at ambient temperature,within which layer 44, as in (ii) above, is now deposited.

The fabrication returns very slowly to ambient during deposition solayer 44 is indeed formed on a cold layer 42. The temperature of thewafer will slowly increase, yet during the first few minutes ofdeposition of the of the rest of the AP1 layer the temperature shouldnot rise very much.

Referring now to FIG. 5, the cooling step is complete and the remainingdeposition steps are carried out at ambient temperatures. However,additional cooling steps are still possible, if so desired, but they arenot shown here. There is now shown the formation of the MgO tunnelingbarrier layer 50 on top of CoFeB layer 44. The MgO layer is between 5and 30 A in thickness. A cooling step can also be applied at this stepin the fabrication, before the MgO deposition is completed. Such acooling step could be in addition to the one previously discussed withthe formation of AP1, or it could be done instead of the one performedwith the deposition of AP1. Note that the MgO may be formed bysputtering deposition of a Mg layer which is then oxidized or by directsputtering from a target of MgO.

Referring next to FIG. 6, there is shown the formation of aferromagnetic free layer 60, generally formed of CoFeB based materialsand formed to a thickness of between 5 and 25 A. The cooling step canalso be applied before the free layer is deposited or while the freelayer is being deposited. If the cooling step is carried out during freelayer deposition, the fabrication is removed to the cooling chamberbefore the free layer is fully deposited. Typically, such amid-deposition cooling would be done when half of the free layer hasbeen deposited, which would be halfway between a free layer that isgenerally between 5 and 25 A in thickness. Normally, the free layer is amulti-layered deposition, such as a layer of Fe₇₀B₃₀ followed by a layerof Co₂₀F₆₀B₂₀. In that case, the cooling would occur before depositionof the Co₂₀Fe₆₀B₂₀.

Referring next to FIG. 7, there is shown the deposition of a MgO cappinglayer 70 on the top of the free layer 60. Again, we note that the MgOmay be formed by oxidizing a layer of Mg or by sputtering a layer ofMgO. The capping layer is between 5 and 30 A in thickness and thecooling step can be applied after completion of the free layerdeposition and before the capping layer deposition. Note that thecooling process can be applied as a series of processes where eachcooling step is applied as noted above, before or during each depositionprocess after first transferring the deposition to the cooling chamber.We note also that the most appropriate fabrication step(s) for applyingthe cooling process may have to be discovered empirically as theparticular nature of the stack seems to affect the beneficial propertiesof the cooling.

Referring finally to FIG. 8, there is shown the deposition of a hardmask 80 which is formed of Ta of approx. 600 A thickness and that willbe used for purposes of patterning the finished stack. We also note thatwe do not indicate any of the various steps of annealing may be requiredas dictated by the necessity of integrating the devices into a largerMRAM system. These anneals do not affect the role of the cooling stepsnor are they required for setting the magnetization of the RKKYinteraction

The beneficial results of this fabrication method can be demonstratedusing reflow tests. As shown in the table below, two otherwise identicalstructures, but one fabricated with and one without a cooling step informing the AP1 layer of a synthetic antiferromagnetic (SAF) pinnedlayer (as described below) show different error rates after a reflowprocess. Reflow is a chip manufacture process where the chip is solderedto the socket by heating a solid layer of solder and causing it toliquify (reflow) and it serves as the strictest requirement for thermalstability of the MTJ stack. Typically, as a result of the reflow processa chip would experience a temperature about 260 C for about 90 s and theinformation stored in the chip before reflow should not be lost duringthe process.

Without cooling With cooling Error rate after reflow 10 ppm 1 ppm

The test is done at the wafer level as follows. A wafer that containsmore than 50 chips is inserted between two metal slabs inside an oven.The temperature of the metal slabs is at least 260 C and the wafer isinside the oven for at least 90 s. Each chip has 10 Mb MTJ units and wasprogrammed to store either information 0 or 1 before the test. We readeach chip after the test to determine the number of MTJ units whosestored information has changed during the baking process. An error rateis then calculated as the number of MTJ units that have changed theirinformation content, divided by the total number of the MTJ devices.

The wafer fabricated without cooling shows an error rate of 10 ppm (10errors out of 1,000,000 devices) whereas the wafer fabricated withcooing shows an error rate of only 1 ppm. The data clearly indicatessignificant improvement of PMA of the pinned layer from the proposedcooling step.

As is finally understood by a person skilled in the art, the preferredembodiments of the present invention are illustrative of the presentinvention rather than limiting of the present invention. Revisions andmodifications may be made to methods, materials, structures anddimensions employed in forming and providing an MTJ MRAM cell deviceusing a process that includes cooling the fabrication at various stages,while still forming and providing such a device and its method offormation in accord with the spirit and scope of the present inventionas defined by the appended claims.

What is claimed is:
 1. A method for fabricating an STT MTJ MRAM (SpinTorque Transfer Magnetic Tunneling Junction Magnetic Random AccessMemory) cell formed as a sequence of material layers, comprising:providing a patterned substrate; forming a seed layer on said substrate;forming a first, or AP2, layer of an RKKY coupled SAF pinned layerstructure on said seed layer; forming an RKKY coupling layer on said AP2layer; forming a first portion of an AP1 layer on said RKKY couplinglayer; cooling said fabrication; forming a second portion of said AP1layer on said first portion of said cooled fabrication, therebycompleting said pinned layer; forming remaining elements of said STT MTJMRAM cell on said pinned layer, said remaining elements comprising atunneling barrier layer, a ferromagnetic free layer a capping layer inthat sequential order.
 2. The method of claim 1 wherein said materiallayers are formed by sputtering in sputtering chambers of a vacuumsealed multi-chamber system and wherein said cooling occurs in aseparate cooling chamber of said system and wherein said fabrication istransferred from said sputtering chambers to said cooling chamber forcooling by thermal contact and then returned to said separate sputteringchambers for the remainder of processing while said fabrication returnsto an ambient temperature.
 3. The method of claim 1 wherein saidfabrication is cooled to a temperature of 60K.
 4. The method of claim 1wherein said seed layer is a layer of NiCr between 30 and 100 A tofacilitate good lattice growth in a (111) direction of said AP2deposition.
 5. The method of claim 1 wherein said AP2 deposition is aCo/X multilayer where X is Ni, Pt, Pd or the like.
 6. The method ofclaim 1 wherein said AP2 deposition provides a PMA (perpendicularmagnetic anisotropy) to the entire fabrication.
 7. The method of claim 1wherein said RKKY coupling layer is a layer of Ru of thickness betweenapproximately 3.5 and 4 A, or a layer of Ir of thickness betweenapproximately 4.5 and 5.5 A or a layer of Mo of thickness betweenapproximately 5 and 6 A.
 8. The method of claim 1 wherein said firstportion of said AP1 layer is a phase breaking layer, typicallyamorphous, used to break the (111) crystal structure of said AP2 layerfrom the (001) crystal structure of the rest of AP1/MgO barrier layer/FLstructure, while they remain magnetically connected through the RKKYinteraction.
 9. The method of claim 1 wherein said second portion ofsaid AP1 layer is a layer of CoFeB formed to a thickness between 5 and25 A.
 10. A method for fabricating an STT MTJ MRAM (Spin Torque TransferMagnetic Tunneling Junction Magnetic Random Access) cell formed as asequence of material layers, comprising: providing a substrate; forminga seed layer on said substrate; forming an RKKY coupled SAF pinned layerstructure on said seed layer; cooling said fabrication; forming an MgOtunneling barrier layer on said RKKY coupled SAF pinned layer structureof said cooled fabrication; forming remaining elements of said STT MTJMRAM cell on said MgO tunneling barrier layer, said remaining elementscomprising a ferromagnetic free layer a capping layer in that sequentialorder.
 11. The method of claim 10 wherein said material layers areformed by sputtering in sputtering chambers of a vacuum sealedmulti-chamber system and wherein said cooling occurs in a separatecooling chamber of said system and wherein said fabrication istransferred from said sputtering chambers to said cooling chamber forcooling by thermal contact and then returned to said separate sputteringchambers for the remainder of processing while said fabrication returnsto an ambient temperature.
 12. The method of claim 10 wherein saidfabrication is cooled to a temperature of 60K.
 13. The method of claim10 wherein said seed layer is a layer of NiCr between 30 and 100 A tofacilitate good lattice growth in a (111) direction of an AP2 depositionof said RKKY pinned layer structure.
 14. The method of claim 10 whereinsaid SAF pinned layer comprises an AP2 layer formed as a deposition ofCo/X multilayers where X is Ni, Pt, Pd or the like, on which is formedan RKKY coupling layer that is a layer of Ru of thickness betweenapproximately 3.5 and 4 A, or a layer of Ir of thickness betweenapproximately 4.5 and 5.5 A or a layer of Mo of thickness betweenapproximately 5 and 6 A, on which is formed an AP1 layer in twoportions, wherein said first portion is a phase breaking layer,typically amorphous, used to break the (111) crystal structure of saidAP2 layer from the (001) crystal structure of the rest of AP1/MgObarrier/FL structure, while they remain magnetically connected throughthe RKKY interaction, and wherein a second portion of said AP1 layer isa layer of CoFeB formed on said first portion to a thickness between 5and 25 A.
 15. The method of claim 10 wherein said MgO tunneling barrierlayer is formed to a thickness between approximately 5 and 30 A inthickness and may be formed on the cooled fabrication by the oxidationof a layer of Mg or by a sputtering deposition using a target of MgO.16. A method for fabricating an STT MTJ MRAM (Spin Torque TransferMagnetic Tunneling Junction Magnetic Random Access) cell formed as asequence of material layers, comprising: providing a substrate; forminga seed layer on said substrate; forming an RKKY coupled SAF pinned layerstructure on said seed layer; forming an MgO tunneling barrier layer onsaid RKKY coupled SyAP pinned layer structure cooling the fabrication;forming a ferromagnetic free layer on said tunneling barrier layer ofsaid cooled fabrication; forming remaining elements of said STT MTJ MRAMcell on said ferromagnetic free layer said remaining elements comprisinga capping layer in that sequential order.
 17. The method of claim 16wherein said material layers are formed by sputtering in sputteringchambers of a vacuum sealed multi-chamber system and wherein saidcooling occurs in a separate cooling chamber of said system and whereinsaid fabrication is transferred from said sputtering chambers to saidcooling chamber for cooling by thermal contact and then returned to saidseparate sputtering chambers for the remainder of processing while saidfabrication returns to an ambient temperature.
 18. The method of claim16 wherein said fabrication is cooled to a temperature of 60K.
 19. Themethod of claim 18 wherein said seed layer is a layer of NiCr between 30and 100 A to facilitate good lattice growth in a (111) direction of anAP2 deposition of said RKKY pinned layer structure.
 20. The method ofclaim 16 wherein said SAF pinned layer comprises an AP2 layer formed asa deposition of Co/X multilayers where X is Ni, Pt, Pd or the like, onwhich is formed an RKKY coupling layer that is a layer of Ru ofthickness between approximately 3.5 and 4 A, or a layer of Ir ofthickness between approximately 4.5 and 5.5 A or a layer of Mo ofthickness between approximately 5 and 6 A, on which is formed an AP1layer in two portions, wherein said first portion is a phase breakinglayer, typically amorphous, used to break the (111) crystal structure ofsaid AP2 layer from the (001) crystal structure of the rest of AP1/MgObarrier/FL structure, while they remain magnetically connected throughthe RKKY interaction, and wherein a second portion of said AP1 layer isa layer of CoFeB formed on said first portion to a thickness between 5and 25 A.
 21. The method of claim 20 wherein said AP2 depositionprovides a PMA (perpendicular magnetic anisotropy) to the entirefabrication.
 22. A method for fabricating an STT MTJ MRAM (Spin TorqueTransfer Magnetic Tunneling Junction Magnetic Random Access) cell formedas a sequence of material layers, comprising: providing a substrateforming a seed layer on said substrate; forming an RKKY coupled SAFpinned layer structure on said seed layer; forming an MgO tunnelingbarrier layer on said RKKY coupled SyAP pinned layer structure partiallyforming a ferromagnetic free layer on said tunneling barrier layer;cooling said fabrication; returning said cooled fabrication to saidsputtering sub-system and completing the formation of said ferromagneticfree layer on said cooled fabrication; forming remaining elements ofsaid STT MTJ MRAM cell on said completed ferromagnetic free layer, saidremaining elements comprising a capping layer in that sequential order.23. The method of claim 22 wherein said material layers are formed bysputtering in sputtering chambers of a vacuum sealed multi-chambersystem and wherein said cooling occurs in a separate cooling chamber ofsaid system and wherein said fabrication is transferred from saidsputtering chambers to said cooling chamber for cooling by thermalcontact and then returned to said separate sputtering chambers for theremainder of processing while said fabrication returns to an ambienttemperature.
 24. The method of claim 23 wherein said fabrication iscooled to a temperature of 60K.
 25. The method of claim 22 wherein saidseed layer is a layer of NiCr between 30 and 100 A to facilitate goodlattice growth in a (111) direction of an AP2 deposition of said RKKYpinned layer structure.
 26. The method of claim 22 wherein said SAFpinned layer comprises an AP2 layer formed as a deposition of Co/Xmultilayers where X is Ni, Pt, Pd or the like, on which is formed anRKKY coupling layer that is a layer of Ru of thickness betweenapproximately 3.5 and 4 A, or a layer of Ir of thickness betweenapproximately 4.5 and 5.5 A or a layer of Mo of thickness betweenapproximately 5 and 6 A, on which is formed an AP1 layer in twoportions, wherein said first portion is a phase breaking layer,typically amorphous, used to break the (111) crystal structure of saidAP2 layer from the (001) crystal structure of the rest of AP1/MgObarrier/FL structure, while they remain magnetically connected throughthe RKKY interaction, and wherein a second portion of said AP1 layer isa layer of CoFeB formed on said first portion to a thickness between 5and 25 A.
 27. The method of claim 26 wherein said AP2 depositionprovides a PMA (perpendicular magnetic anisotropy) to the entirefabrication.
 28. A method for fabricating an STT MTJ MRAM (Spin TorqueTransfer Magnetic Tunneling Junction Magnetic Random Access) cell formedas a sequence of material layers, comprising: providing a substrate;forming a seed layer on said substrate; forming an RKKY coupled SyAPpinned layer structure on said seed layer; forming an MgO tunnelingbarrier layer on said RKKY coupled SyAP pinned layer structure; forminga free layer on said MgO tunneling barrier layer; cooling saidfabrication; returning said cooled fabrication to said sputteringsub-system and forming a capping layer on said ferromagnetic free layerof said cooled fabrication.
 29. The method of claim 28 wherein saidmaterial layers are formed by sputtering in sputtering chambers of avacuum sealed multi-chamber system and wherein said cooling occurs in aseparate cooling chamber of said system and wherein said fabrication istransferred from said sputtering chambers to said cooling chamber forcooling by thermal contact and then returned to said separate sputteringchambers for the remainder of processing while said fabrication returnsto an ambient temperature.
 30. The method of claim 29 wherein saidfabrication is cooled to a temperature of 60K.
 31. The method of claim28 wherein said seed layer is a layer of NiCr between 30 and 100 A tofacilitate good lattice growth in a (111) direction of an AP2 depositionof said RKKY pinned layer structure.
 32. The method of claim 28 whereinsaid SAF pinned layer comprises an AP2 layer formed as a deposition ofCo/X multilayers where X is Ni, Pt, Pd or the like, on which is formedan RKKY coupling layer that is a layer of Ru of thickness betweenapproximately 3.5 and 4 A, or a layer of Ir of thickness betweenapproximately 4.5 and 5.5 A or a layer of Mo of thickness betweenapproximately 5 and 6 A, on which is formed an AP1 layer in twoportions, wherein said first portion is a phase breaking layer,typically amorphous, used to break the (111) crystal structure of saidAP2 layer from the (001) crystal structure of the rest of AP1/MgObarrier/FL structure, while they remain magnetically connected throughthe RKKY interaction, and wherein a second portion of said AP1 layer isa layer of CoFeB formed on said first portion to a thickness between 5and 25 A.
 33. The method of claim 32 wherein said AP2 depositionprovides a PMA (perpendicular magnetic anisotropy) to the entirefabrication.
 34. A method for fabricating an STT MTJ MRAM (Spin TorqueTransfer Magnetic Tunneling Junction Magnetic Random Access) cell formedas a sequence of material layers, comprising: providing a substrate;forming a seed layer on said substrate; forming a first, or AP2, layerof an RKKY coupled SyAP pinned layer structure on said seed layer;forming a RKKY coupling layer on said AP2 layer; forming a first portionof an AP1 layer on said RKKY coupling layer; cooling said fabricationfor a first time; forming a second portion of said AP1 layer on saidcooled first portion; cooling said fabrication for a second time;forming a tunneling barrier layer on said SyAP pinned layer; coolingsaid fabrication for a third time; forming a ferromagnetic free layer onsaid tunneling barrier layer; cooling said fabrication for a fourthtime; forming a capping layer on said ferromagnetic free layer.
 35. Themethod of claim 34 wherein said material layers are formed by sputteringin sputtering chambers of a vacuum sealed multi-chamber system andwherein each of said four cooling processes occurs in a separate coolingchamber of said system and wherein said fabrication is transferred fromsaid sputtering chambers to said cooling chamber for cooling by thermalcontact and then returned to said separate sputtering chambers for theremainder of processing while said fabrication returns to an ambienttemperature.
 36. The method of claim 34 wherein said fabrication iscooled to a temperature of 60K during each cooling process.
 37. Themethod of claim 34 wherein said first portion of said AP1 layer is aphase breaking layer, typically amorphous, used to break the (111)crystal structure of said AP2 layer from the (001) crystal structure ofthe rest of AP1/MgO barrier/FL structure, while they remain magneticallyconnected through the RKKY interaction.
 38. The method of claim 34wherein said second portion of said AP1 layer is a layer of CoFeB formedto a thickness between 5 and 25 A.
 39. The method of claim 34 whereinsaid seed layer is a layer of NiCr between 30 and 100 A to facilitategood lattice growth in a (111) direction of an AP2 deposition of saidRKKY pinned layer structure.
 40. The method of claim 34 wherein said AP2is Co/X multilayer where X is Ni, Pt, Pd or the like.
 41. The method ofclaim 34 wherein said AP2 deposition provides a PMA (perpendicularmagnetic anisotropy) to the entire fabrication.